1. Field of Invention
The present invention is related to a semiconductor device. More particularly, the present invention relates to a super junction semiconductor device.
2. Description of Related Art
Power semiconductor devices are used in many fields such as home electric appliance, automobile, electric train and electric transmission. Power semiconductor devices are applied to inverter systems and power supply circuits as switching mode devices. In these applications, under specific reverse blocking capability, lowering the specific on-resistance of power semiconductor device is necessary for reducing power losses in the systems. There had several versions of power semiconductor devices been published, such as planar gate MOSFET, trench gate MOSFET, lateral MOSFET and Vertical MOSFET, in order to improve the trade-off relationship of reverse blocking voltage and the specific on-resistance. More precisely, the definition of the trade-off relationship is that when increasing the reverse blocking voltage, the specific on-resistance will increase dramatically.
In view of solving the above sensitive relationship, super junction structure is used for designing the drift region of a power MOSFET. Due to its uniform lateral depletion of highly doped alternating P-type and N-type layer region, having outstanding reverse voltage sustainability and low specific on-resistance is no longer a problem. So far, super junction has been the most creative and important concept in power semiconductor device field. However, there are still several drawbacks of conventional super junction devices.
The major drawback is that while the development of conventional super junction devices to obtain the best trade-off between the reverse blocking voltage and specific on-resistance is hard to achieve, besides that shrinking the feature size without affecting the device characteristics is also difficult. Because conventional super junction devices suffer sever auto-doping effect after thermal process, which leads to degradation in the most important device parameters, such as reverse blocking voltage and the specific on-resistance. Especially when the P-type and N-type layer concentration is highly doped for a lower specific on-resistance performance, the auto-doping phenomenon will be even more drastic.
The deviation of the concentration will cause charge-imbalance to occur within the super junction P-type and N-type layers, at the same time the layer width might vary from the beginning design. The more impurity concentration deviation that a super junction has, the more device characteristics degradation it will obtain. Although much effort has been put into the feature size reduction while maintaining the desired breakdown voltage, it has been understood that there is a limit. For the foregoing reasons, the inventor realizes that there is a certain need for a new super junction device that may improve the above-mentioned problems.